To other, smaller beings that find their way into the interior of the shell, the conch reacts less tolerantly. Current-borne eggs of many sea creatures, larvae of marine worms, minute shrimp or even fish, or non-living particles like grains of sand, may swim or drift inside and, lodging on shell or mantle, set up an irritation. To this the conch responds with ancient defenses, acting to wall off the particle so that it can no longer irritate delicate tissues. The glands of the mantle secrete about this nucleus of foreign matter layer after layer of mother-of-pearl—the same lustrous substance that lines the inside of the shell. In this way the conch creates the pink pearls sometimes found within it.
The human swimmer drifting idly above the turtle grass—if he is patient enough and observant enough—may see something of other lives being lived above the coral sand, from which the thin flat blades of grass reach upward and sway to the motion of the water, leaning shoreward on a flooding tide and seaward on the ebb. If, for example, he looks very carefully he may see what he had thought to be a blade of grass (so perfectly did it simulate one by form and color and movement) detach itself from the sand and go swimming through the water. The pipefish—an incredibly long, slender, and bony-ringed creature that seems quite unfishlike—swims between the grasses slowly and with deliberate movement, now with its body held vertically, now leaning horizontally into the water. The slim head with its long, bony snout is thrust with probing motions into clusters of turtle grass leaves or down among the roots, as the fish searches for small food animals. Suddenly there is a quick, inflating motion of the cheek, and a tiny crustacean is sucked in through the tube-like beak, as one would suck a soda through a straw.
The pipefish begins life in a strange manner, being developed, nurtured, and reared beyond the stage of helpless infancy by the male parent, who keeps his young within a protective pouch. During the mating act of the pair, the ova are fertilized and are placed in this pouch by the female; there they develop and hatch, and to this marsupium the young may return again and again in moments of danger, even long after they are able to swim out into the sea at will.
So effective is the camouflage of another inhabitant of the grass—the sea horse—that only the sharpest eye can detect one at rest, its flexible tail gripping a blade of grass and its bony little body leaning out into the currents like a piece of vegetation. The sea horse is completely encased in an armor composed of interlocking bony plates; these take the place of ordinary scales and seem to be a sort of evolutionary harking back to the time when fish depended on heavy armor to protect them from their enemies. The edges of the plates, where they join and interlock, are produced into ridges, knobs, and spines to form the characteristic surface pattern.
Sea horses often live in vegetation that is floating rather than rooted; such individuals may then become part of that steady northward drift bearing plants, associated animals, and the larvae of countless sea forms into the open Atlantic and eastward toward Europe, or into the Sargasso Sea. Such sea-horse voyagers in the Gulf Stream sometimes are carried ashore on the southern Atlantic coast along with bits of wind- and current-borne sargassum weed to which they cling.
In some of the turtle-grass jungles all of the smaller inhabitants seem to borrow a protective color from their surroundings. I have dragged a small dredge in such a place and found, entangled in the handfuls of grass that came up, dozens of small animals of different species, all an amazing, bright green hue. There were green spider crabs with extremely long, jointed legs. There were small shrimp, also grass-green. Perhaps the most fantastic touch was contributed by several baby cowfish. Like their elders, whose remains one often finds in the debris of the high-tide line, these little cowfish were encased in bony boxes that held head and body in an inflexible case, from which fins and tail protruded as the only movable parts. From tip of tail to the little forward-projecting, bovine horns, these small cowfish were the green of the grass in which they lived.
Especially where they border the channels between the Keys, the shoals carpeted with marine grasses are visited from time to time by sea turtles, which live in some numbers about the outer reef. The hawksbill wanders far out to sea, and seldom turns landward; but the green and loggerhead turtles often swim into the shallow waters of Hawk Channel or seek the passages between the Keys, where the tides race swiftly. When these turtles visit the grassy shoals they are usually seeking those inflated sand dollars, the sea biscuits, whose home is among the grass, or they may seize some of the conchs. Apart from others of their own kind, the conchs probably have no more dangerous enemies than the big turtles.
However far they may wander, loggerhead, green, or hawksbill all must return to land for the spawning season. There are no spawning places on the Keys of coral rock or limestone, but on some of the sand keys of the Tortugas group the loggerhead and the green turtles emerge from the ocean and lumber over the sand like prehistoric beasts to dig their nests and bury their eggs. The chief spawning places of the turtles, however, are on the beaches of Cape Sable and other sand strands of Florida, and farther north in Georgia and the Carolinas.
If the predatory visits of the big turtles to the sea-grass meadows are sporadic, it is far otherwise with the ceaseless, day-by-day preying of the various conchs, one upon another, and all upon mussels or oysters, sea urchins and sand dollars. The chief predator of all the conchs is the dusky-red spindle-shaped one called the horse conch. One has only to see it feeding to realize how powerful it is; when the massive body, brick-red like the shell, is extended to enfold and overwhelm its prey, it seems impossible to believe that so much flesh can ever be drawn back into the shell again. Even the king crown conch, itself a predator on many other conchs, is no match for it. No other American gastropods approach its size. (One-foot individuals are fairly common and the giants of its kind are two feet long.) The big cask shells also are victims of the horse conch, while they themselves feed usually on urchins. Yet I have felt little awareness of this relentless predation on making a casual visit to the habitat of the conchs. There are long periods of somnolence and repletion, and the grassy world by day seems a peaceful place. A conch gliding over the coral sand, a sea cucumber burrowing sluggishly among the roots of the grasses, or the dark and swiftly fleeting forms of sea hares in sudden passage may be the only visible signs of life and motion. For by day life is in retreat; life is buried and hidden in crevices and corners of ledge and rock; life has crept under or within the shelter of sponge or gorgonian or coral or empty shell. In the shallow waters of the shore, many creatures must avoid the penetrating sunlight that irritates sensitive tissues and reveals prey to predator.
But that which seems quiescent—a dream world inhabited by-creatures that move sluggishly or not at all—comes swiftly to life when the day ends. When I have lingered on the reef flat until dusk fell, a strange new world, full of tensions and alarms, has replaced the peaceful languor of the day. For then hunter and hunted are abroad. The spiny lobster steals out from under the sheltering bulk of a big sponge and flashes away across the open water. The gray snapper and the barracuda patrol the channels between the Keys and dart into the shallows in swift pursuit. Crabs emerge from hidden caverns; sea snails of varied shape and size creep out from under rocks. In sudden movements, swirling waters, and half-seen shadows that dart across my path as I wade shoreward, I sense the ancient drama of the strong against the weak.